Abstract-This paper presents the design and performance analysis of an Improved Differential Chaos Shift Keying (I-DCSK) system. Instead of sending reference and data carrier signals in two time slots as in conventional DCSK scheme, in the improved design, a time reversal operation is used to generate an orthogonal reference signal to the data carrier signal and then sum up these two sequences into one time slot, prior to transmission. This operation reduces the bit duration to half, which doubles data rate and enhances spectral efficiency. At the receiver, the received signal is correlated to its time reversed replica and is summed over the bit duration. The new system design proposed in this work replaces the delay circuit used in conventional DCSK systems by time reversal operations. Moreover, the theoretical bit error rate expressions for AWGN and multipath fading channels are analytically studied and derived. The proposed I-DCSK system is compared to the conventional DCSK and Quadrature Chaos Shift Keying (QCSK) schemes. Finally, to validate accuracy, simulation results are compared to relevant theoretical expressions.

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Abstract-One of the major drawbacks of the conventional Differential Chaos Shift Keying (DCSK) system is the addition of channel noise to both the reference signal and the data bearing signal, which deteriorates its performance. In this paper, we propose a noise reduction DCSK (NR-DCSK) system as a solution to reduce the noise variance present in the received signal in order to improve performance. For each transmitted bit, instead of generating β different chaotic samples to be used as a reference sequence, β/P chaotic samples are generated and then duplicated P times in the signal. At the receiver, each P identical samples are averaged and the resultant filtered signal is correlated to its time delayed replica to recover the transmitted bit. This averaging operation of size P reduces the noise variance and enhances the performance of the system. Theoretical bit error rate expressions for AWGN and multipath fading channels are analytically studied and derived. Computer simulation results are compared to relevant theoretical findings to validate the accuracy of the proposed system and to demonstrate the performance improvement compared to the conventional DCSK, the Improved DCSK (I-DCSK) and the Differential Phase Shift Keying (DPSK) systems.

Abstract-Data rate and energy efficiency decrement caused by the transmission of reference and data carrier signals in equal portions constitute the major drawback of differential chaos shift keying (DCSK) systems. To overcome this dominant drawback, a short reference DCSK system (SR-DCSK) is proposed. In SR-DCSK, the number of chaotic samples that constitute the reference signal is shortened to R such that it occupies less than half of the bit duration. To build the transmitted data signal, P concatenated replicas of R are used to spread the data. This operation increases data rate and enhances energy efficiency without imposing extra complexity onto the system structure. The receiver uses its knowledge of the integers R and P to recover the data. The proposed system is analytically studied and the enhanced data rate and bit energy saving percentages are computed. Furthermore, theoretical performance for AWGN and multipath fading channels are derived and validated via simulation. In addition, optimising the length of the reference signal R is exposed to detailed discussion and analysis. Finally, the application of the proposed short reference technique to the majority of transmit reference systems such as DCSK, multicarrier DCSK, and quadratic chaos shift keying enhances the overall performance of this class of chaotic modulations and is, therefore, promising.

Abstract-A new non-coherent scheme called Permutation Index Differential Chaos Shift Keying (PI-DCSK) modulation is proposed in this paper. This original design aims to enhance data security, energy and spectral efficiencies, compared to its rivals. In the proposed PI-DCSK scheme, each data frame is divided into two time slots in which the reference chaotic signal is sent in the first time slot and a permuted replica of the reference signal multiplied by the modulating bit is sent in the second time slot. In particular, the bit stream is divided at the transmitter into blocks of n + 1 bits, where n mapped bits are used to select one of the predefined reference sequence permutations, while a single modulated bit is spread by the permuted reference signal just mentioned. At the receiver side, the reference signal is recovered first, then all permuted versions of it are correlated with the data-bearing signal. The index of the correlator output with maximum magnitude will estimate the mapped bits, while the output content of the corresponding correlator is compared to a zero threshold to recover the modulated bit. Moreover, a new multiple access (MA) method based on the proposed scheme is described and analysed. Analytical expressions for the error performance in single-user and multi-user environments are derived for additive white Gaussian noise (AWGN) and multipath Rayleigh fading channels, respectively. Furthermore, the performance of the proposed PI-DCSK system is analysed and compared with other non-coherent chaotic modulation schemes and is found to be promising.Index Terms-Chaos-based communication systems, permutation index differential chaos shift keying (PI-DCSK), bit error rate (BER), non-coherent detection, multiple access (MA).